Heat exchange element and heat exchanger produced therewith

ABSTRACT

A heat exchange element is described having adjacent, heat-transferring, smooth walls ( 1 ) which, between each other, delimit flow channels ( 4 ) with preselected channel widths (B) for at least one fluid and are provided with undulations ( 6 ) which protrude on both sides and transversely relative to imaginary central planes ( 7 ), said undulations having preselected wavelengths (λ) as well as apexes ( 9   a,    9   b ) with radii of curvature (R) and apex spacings (W) measured transversely relative to the central planes ( 7 ). According to the invention inequalities 0.1≦B/W≦0.55 and R≧1.2 B apply at least partially to ratios of channel width (B)/apex spacing (W) and channel width (B)/radius of curvature (R) ( FIG. 2 ).

FIELD OF THE INVENTION

The invention relates to a heat exchange element having adjacent,heat-transferring, smooth walls which, between each other, delimit flowchannels with preselected channel widths for at least one fluid and areprovided with undulations which protrude on both sides and transverselyrelative to imaginary central planes, said undulations havingpreselected wavelengths and apexes with radii of curvature and apexspacings measured transversely relative to the central planes. Theinvention also relates to a heat exchanger provided with such a heatexchange element.

BACKGROUND OF THE INVENTION

Heat exchange elements having adjacent, smooth walls which delimit,between each other, flow channels are, according to the purpose of use,components of pipe, plate or ribbed heat exchangers and/or areconfigured as fin arrangements or lamellae (corrugated ribs). They areused e.g. in automotive vehicles, compressors, washer-dryers,air-conditioning and refrigeration plants or refrigeration dryers forcompressed air plants and also used for cooling electronic componentsand in numerous machines, such as e.g. building, agricultural andforestry machines. The flow channels of heat exchange elements of thistype are generally delimited by smooth, flat walls through which,according to the purpose of use, a fluid, such as e.g. air, water or oilflows, and serve for the purpose of transferring heat to the respectivefluid or respectively absorbing heat therefrom. In the flow channels,laminar or turbulent flows are thereby formed which, in the zonesabutting on the walls, lead to characteristic boundary layers in whichthe throughflowing fluids are located in the ideal case of a laminarflow substantially in a stationary manner. In comparison thereto thefluids are moved forwards within the central core zones of the flowchannels at the greatest speed.

The formation of the boundary layers has the result that the wallsurfaces which are present are only incompletely usable for heattransfer and that the achievable heat exchange outputs are small. It hastherefore already been known for a long time (DE-PS 596 871) to providethe walls of the flow channels with embossings which emerge from thewall surface and generate turbulence, said embossings being parallel orat acute angles to the flow axis. As a result, the parts of the fluidflows close to the walls are divided repeatedly with formation of localturbulences and the otherwise forming boundary layers are disrupted anddestroyed. As a consequence thereof, a noticeable improvement in theheat exchange output occurs.

The described embossings which form turbulence can however lead to twodisadvantages. On the one hand they are able not only to deflect theparts of the flow close to the walls in the direction of the core zonesand consequently to increase the heat exchange output but also to reducethe flow cross-sections and consequently to lead to an undesiredincrease in the pressure losses occurring along the flow channels. As aresult, the volume flows passing along the flow channels arecorrespondingly reduced with natural convection, whereas, with forcedconvection, more powerful fans, pumps or the like are required in orderto maintain a preselected volume flow. On the other hand, embossings ofthe described type can have a tendency to become soiled because of theircross-sectional forms, in particular if they are used e.g. in coolersfor agricultural, forestry and building machines or vehicles or inhousehold washer-dryers and if the fluid is process air and/or coolingair.

Heat exchange elements of the initially described type have thereforealso already become known (e.g. U.S. Pat. No. 3,907,032) in which thewalls delimiting the flow channels are provided with undulations whichextend transversely relative to the flow direction or are configured ina continuous undulating shape. Even with such heat exchange elements, nooptimum results have been achieved to date since either an unfavourableoutput/pressure loss ratio is obtained or, in the attempt to optimisethis, an increased tendency to become soiled. This applies even when theundulations are provided with predetermined dimensions or comparativelycomplicated forms (e.g. DE 195 03 766 A1, EP 1 357 345 A2). Likewiseknown heat exchange elements, in which adjacent walls are provided withdifferently structured undulations (e.g. DE 102 18 274 A1), have thedisadvantage above all that their flow channels have greatly varyingcross-sections which is not useful for reducing pressure losses.

SUMMARY OF THE INVENTION

It is an object of the present invention to design the heat exchangeelement described above such that the heat exchange output (power) isenhanced and the pressure losses are reduced.

It is another object of the present invention to increase the ratio ofheat exchange output to pressure loss of the heat exchange elementmentioned above.

Another object of the present invention is to design the heat exchangeelement such that a reduction in the tendency to become soiled isachieved, particularly in case of heat exchange with gaseous fluids.

Yet another object of the present invention is to provide a heatexchanger with an increased ratio of heat exchange output to pressureloss and at the same time with a reduced tendency to become soiled.

These and other objects of the present invention are obtained by meansof a heat exchange element of the type mentioned above and beingcharacterized in that inequalities 0.1≦B/W≦0.55 and R≧1.2 B apply atleast partially to ratios of channel width/apex spacing and channelwidth/radius of curvature. The invention further provides a heatexchanger having such a heat exchange element.

By means of the invention, increased heat exchange outputs are achieved,in particular in conjunction with gaseous fluids such as e.g. airwithout correspondingly increased pressure losses requiring to be takeninto account. In addition, the undulations are configured such that thetendency to become soiled is low. The heat exchange elements accordingto the invention and heat exchangers equipped therewith are thereforevery suitable in particular for applications in coolers foragricultural, forestry and building machines and also in washer-dryers,charge coolers of vehicles or devices for cooling electronic components.

Further advantageous features of the invention are revealed in thedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective representation of a heat exchange element accordingto the invention which has undulating walls in the form of a lamella(corrugated rib);

FIG. 2 an enlarged plan view on a plurality of adjacent walls of theheat exchange element according to FIG. 1, configured according to theinvention;

FIG. 3 a plan view corresponding to FIG. 2 on a single wall of the heatexchange element according to FIG. 1;

FIG. 4 to 6 plan views corresponding to FIG. 3 on three furtherembodiments of walls according to the invention for a heat exchangeelement;

FIG. 7 a plan view corresponding to FIG. 2 on four heat exchangeelements with different total lengths;

FIG. 8 a plan view corresponding to FIG. 3 on a single wall of a furtherembodiment of a heat exchange element according to the invention;

FIGS. 9 and 10 perspective views of a flat pipe heat exchanger and of aheat exchanger with a plate-like construction, both being provided withheat exchange elements according to the invention; and

FIG. 11 a perspective representation of a ribbed cooling body providedwith a heat exchange element according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 to 3 show a heat exchange element according to the invention andaccording to an embodiment deemed to be the best one up to now. The heatexchange element comprises a plurality of adjacent, heat-transferringwalls 1 which are preferably disposed parallel to each other. The walls1 are formed by thin plates which have a height D (FIG. 1) and athickness S (FIG. 2) and are connected to each other in a meanderingshape at their upper and lower longitudinal edges in FIG. 1 by upper andlower, likewise plate-shaped connecting portions 2 a, 2 b. In alongitudinal direction of the heat exchange element indicated by arrows3, a plurality of adjacent flow channels 4 for a fluid, which haveU-shaped cross-sections, is consequently produced, these flow channels 4respectively being delimited by two adjacent walls 1 and, in addition inFIG. 1, alternately by an upper or lower connecting portion 2 a, 2 b.

The flow channels 4 are open at their front and rear ends in thelongitudinal direction. The regions of the flow channels 4 which areopen at the top or bottom in FIG. 1 transversely relative to thelongitudinal direction are in contrast closed as a rule by a functionalpart of a heat exchanger or the like, not shown, when using the heatexchange element according to FIG. 1. The flow channels 4 serve for thepurpose to guide a fluid (e.g. air, water, oil or the like) flowingthrough in the direction of the arrows 3 or in the opposite direction,said fluid thereby coming into heat-exchanging contact with the walls 1and the connecting portions 2 a, 2 b and therefore being cooled orheated according to the case.

The walls 1 comprise materials which are normal in heat exchangers (e.g.a metal such as aluminium or copper, graphite, a plastic material or thelike). They are in addition preferably smooth, i.e. are provided attheir broad sides 5 a, 5 b which are orientated towards the flowchannels 4 and disposed between the upper and lower edges, neither withknobs, flakes, scales or other embossings nor with openings in the formof cuts, holes or the like. Consequently, disruptive dirt-collectingcorners or the like are extensively or entirely avoided in the flowchannels 4.

FIG. 2 shows four adjacent walls 1 in plan view, the connecting portions2 a, 2 b (FIG. 1), which are not essential here, being omitted in orderto avoid lack of clarity. It is assumed in the embodiment that all thewalls 1 have an essentially identical configuration and are situatedopposite each other in pairs with their broad sides 5 a and 5 b formingthe flow channels 4.

In order to improve the heat transfer between the walls 1 and the fluidwhich is reduced by slowly-moving or entirely immobile boundary layers,the walls 1 are provided in a manner known per se with undulations orsinusoidal undulations 6, these undulations 6 being obtained bydeformation of the plates forming the walls 1 about lines which extendaccording to FIG. 1 in the direction of their height D and essentiallyparallel to the broad sides 5 a, 5 b of the walls 1. In addition, inparticular FIG. 3 shows that the undulations 6 extend alternately on oneor the other side of an imaginary central plane 7 indicated by a brokenline, said central plane corresponding to the central plane of theoriginal, non-deformed, plane-parallel plate. As a result, theundulations 6 respectively contain a first half-wave 6 a leading in theflow direction 3 (FIG. 3) and a second half-wave 6 b trailing in theflow direction 3, respectively, the first half-wave 6 a being disposedon one side and the second half-wave 6 b on the other side of thecentral plane 7 and both half-waves 6 a, 6 b abutting against each otheror being connected to each other along a connecting line 8 situated inthe central plane 7. As a result, the half-waves 6 a respectively forman embossing which protrudes in one direction from the central plane 7of the wall 1, whilst the half-waves 6 b respectively represent anembossing which protrudes in the opposite direction from the centralplane 7 of the wall 1. These embossings or half-waves form continuouslyclosed surfaces without open slots or other interruptions.

In the embodiment, the undulations 6 in all the walls 1 of the heatexchange element according to FIG. 1 are configured in the same way andare disposed parallel and without offset in the flow direction 3, i.e.with a constant clear spacing relative to each other so that the flowchannels 4 according to FIG. 2 essentially continuously have the samechannel width corresponding to a dimension B. It is revealed further inFIGS. 2 and 3 that the undulations 6 have upper and lower apexes 9 a and9 b which are curved about lines situated in the central planes 7. Theapex spacings measured transversely relative to the central planes 7have, according to FIGS. 2 and 3, a dimension W, measured between thehigh or low points of imaginary central lines of the walls 1. Inaddition, the undulations 6 in the region of the apexes 9 a, 9 b haverespectively radii of curvature corresponding to a dimension R in FIGS.2 and 3.

According to the invention, the heat exchange element is configured suchthat, on the one hand, an increase in output is achieved by increasingthe heat-exchanging surfaces per unit of volume, and on the other hand,due to great radii of curvature within the flow channels 4, both thepressure loss and the tendency to become soiled is kept within limits.

In order to increase the output, it is provided to choose the channelwidth B of the heat exchange element according to the inventioncorresponding to the inequality B≦0.55 W significantly less than theapex spacing W. A ratio of B/W has proved to be advantageous whichfulfils the inequality 0.1≦B/W≦0.55, the inequality 0.35≦B/W≦0.50 beingmaintained particularly preferably. It is consequently achieved that thefluid flow, as indicated in FIG. 2 by arrows, is deflected in the regionof each half-wave 6 a, 6 b instead of being conducted withoutsubstantial deflection and practically in a straight line through theflow channels 4, as applies to conventional heat exchange elements inwhich the channel width B is greater than the apex spacing W or at bestslightly smaller than this. The dimension B≦0.55 W hat the result thatthe undulations 6 corresponding to FIG. 2 overlap to a great extent in adirection transversely to the central planes 7, i.e. each half-wave 6 a,6 b protrudes deeply into the half-wave 6 a, 6 b of the adjacent wall 1which is located thereabove or therebelow, and in fact by somewhat morethan corresponds to the position of the relevant central plane 7. Theconsequently achieved tighter packing or smaller pitch or spacing T(FIG. 1) of the walls 1 leads to a significant increase in output of theheat exchange element per unit of volume.

In order to obtain despite the undulations 6 and the condition B≦0.55 Wpercentage pressure losses which are—as compared with flat walls—at bestsmaller than the percentage increases in output obtained by theundulations 6, it is proposed to choose the radii of curvature R in theregion of the apexes 9 a, 9 b to be comparatively large. According tothe invention, values of R have proved to be favourable for which theinequality R≦1.3 B applies. It is particularly advantageous if the ratioB/R of the inequality 0≦B/R≦0.75 and even more preferred the inequality0.2≦B/R≦0.55 is fulfilled. The advantage is consequently achieved thatthe deflection of the fluid in the flow channels 4 is effected in factnoticeably but comparatively gently, in comparison to configurations inwhich the radii of curvature are at most 3 mm or even substantiallylower, which results in substantially smaller pressure losses.

The configuration according to the invention of the undulations 6 andthe channel widths B makes it possible in addition to use larger anglesα and β (FIG. 3) for the portions of the undulations, 6 which start fromthe central planes 7 and rise or, respectively, slope down and lead intothe central planes 7. As a result, the advantage is achieved that, inthe case of equal channel widths B and wavelengths λ, greateroverlappings of the undulations 6 or half-waves 6 a, 6 b are possibleand hence the heat-exchanging surfaces can be enlarged. However, theangles α and β should preferably not be greater than 40°.

Furthermore, the heat exchange elements are provided with dimensionsλ≧15 mm or ≧4 W, preferably e.g. 18 mm, 2.4 mm≦R≦6.5 mm, α=β=approx.30°, 0.08 mm≦S≦5 mm and B<2 mm, these dimensions of course representingmerely examples from which a deviation can be made in the individualcase according to requirement.

Finally, FIG. 3 above all shows that the rising and falling portions ofthe half-waves 6 a, 6 b are preferably straight or flat and areconnected in the region of the apexes 9 a, 9 b by curved portions havingthe radii R. As a result, a triangular appearance is produced for thewalls 1, merely the apexes 9 a, 9 b being convex, i.e. rounded towardsthe central planes 7.

FIG. 4 shows a wall which corresponds essentially to the embodimentaccording to FIG. 3. There is a difference only in that the curvedportions situated in the apexes have different radii of curvature R1 toR4. All the radii R1 to R4 are situated within the above-indicatedregions.

FIG. 5 shows a wall 12 of a heat exchange element according to theinvention, said wall having exclusively straight and flat portions. Inparticular a first half-wave 14 a of an undulation 14 has a flat portion15 which rises in a straight line at the angle α, a flat section 16which falls in a straight line at the angle β and a flat portion 17which connects both and is disposed in the region of the apex, saidportion 17 being disposed preferably parallel to the central plane 7. Inthis case, R=∞ applies to the radius of curvature. With respect to thedimensioning of the portion 17, it should be taken, however, intoaccount that it has a length (e.g. L₁) which is so large that the tworelevant ends of the portions 15, 16 could be connected optionally alsoby an imaginary curved portion 18, indicated in broken lines, the radiusof curvature of which is situated in the above-indicated regions. As aresult, comparatively long portions 15 and 16 can also be achieved, asis desired for a good overlapping of the half-waves 14 a, 14 b withoutthe occurence of pressure losses which are not tolerable. The lengths ofthe straight portions 17 can all be of the same length or, as indicatedin FIG. 5 by dimensions L₁ to L₄, of different lengths.

According to a further embodiment, not shown, it is possible to replacethe curved portions 18, shown in broken lines in FIG. 5, by a pluralityof short portions which approximate to the portions 18 shown in brokenlines in the manner of a polygon. The same measurements as in FIG. 3 areproduced for the consequently obtained, imaginary radii of curvature.

FIG. 6 shows finally an embodiment of a wall 20 according to theinvention which has half-waves 21 a, 21 b which are configuredcorresponding to the above description and are connected to each otherby straight, flat portions 22 which are situated preferably in thecentral planes 7 and which can have the same or different lengths. Inaddition, FIG. 6 shows that the half-waves 21 a, 21 b can have differentapex heights W₁ and W₂ relative to the central planes 7, which apexheights sum up to the apex spacing W. Correspondingly different apexheights W₁, W₂ can also be provided in the embodiments according to FIG.1 to 5 without deviating from the indicated dimensions for the apexspacing W.

FIG. 7 shows four heat exchange elements 23 to 26 according to theinvention, which are distinguished by different total lengths asmeasured in the flow direction 3, and are obtained by a different numberof three, four, five or six undulations following one behind the otherin the flow direction 3. It is thereby evident that the undulations canhave different shapes and/or dimensions. In addition, FIG. 7 shows thatthe flow channels 4 preferably have inlet and/or outlet ends 27, 28which are arranged parallel to the central planes, not shown here, inorder that fluid is diverted also when entering the heat exchangeelement 23 to 27 or when flowing out of the latter, in a manner whichdoes not assist pressure losses.

Furthermore, it can be expedient within the scope of the invention tolet the wave lengths λ and/or the apex spacings W, in the flow direction3, become gradually larger or—as is shown in the embodiment according toFIG. 8 by wavelengths λ₁, λ₂ and λ₃ and the apex spacings W₃, W₄ andW₅—gradually smaller. It is consequently possible to achieve, in thedirection of flow, a turbulence formation which becomes gradually moreintensive and a heat transfer output which hence becomes graduallylarger. In addition, FIG. 8 shows that the half-waves on both sides oftheir apexes can also have an asymmetrical configuration.

The described heat exchange elements can be applied in different ways.For example, FIG. 9 shows a flat tube (pipe) heat exchanger with flattubes 31 between which heat exchange elements configured according toFIG. 1 to 8 are disposed in the form of lamellae 32 (corrugated ribs).The lamellae 32 are folded here in a meandering shape analogously toFIG. 1 and provided with lateral walls 33 which are connected to eachother by essentially flat upper or lower connecting portions 34 a, 34 b.The lateral walls 33 are provided according to the invention withundulations which are configured analogously to FIG. 3 to FIG. 8. Thelateral walls 33 respectively delimit flow channels through which forexample a gaseous cooling medium flows in order to cool a liquid fluidwhich flows in the flat pipes 31. The flow directions are indicated byway of example by arrows 35, 36.

FIG. 10 shows a heat exchanger in the normal plate-like construction.The heat exchanger contains a multiplicity of rectangular plates 38which are disposed parallel and in a stack one above the other, saidplates being kept at a spacing at their edges alternately by profiles 39which extend parallel to the long sides and profiles 40 which extendparallel to the short sides. As a result, flow channels 41, which extendin the longitudinal direction as well as flow channels 42, which extendstransversely thereto are produced between the plates 38 and profiles 39or 40 for guiding a first fluid and a second fluid. In addition,schematically indicated fin plates or lamellae 43, 44, which areconfigured here with a zigzag or undulating configuration instead of ameandering one, are disposed in the flow channels 41 and/or 42, saidlamellae serving to improve the heat transfer between the two fluids. Inaddition, one of the two normal collection tanks (headers) is indicatedwith the reference number 45, by means of which the first fluid, e.g. aliquid, is distributed to the flow channels 41 or is removed therefrom.The plates 38, profiles 39 and 40, lamellae 43 and 44 and alsocollection tanks 45 can be connected to each other in a manner known perse, e.g. by glueing or soldering. The lamellae 43 and/or 44 have lateralwalls 46 which are configured corresponding to FIG. 1 to 8. The flowdirections for the fluids are indicated by way of example by arrows.

FIG. 11 shows finally a heat exchange element with a plurality ofheat-transferring walls 48 which are disposed parallel to each other andare formed by thin plates deformed in an undulating shape. The walls 48are attached by lower narrow sides by means of soldering, glueing orotherwise to a base plate 49 which connects the walls 48 securely toeach other, and, starting from the base plate 49, have a height D. Twobroad sides 50 of the walls 48 which are situated opposite each otherrespectively in pairs delimit a flow channel 51 for a fluid. The baseplate 49 abuts for example on an electronic component to be cooled sothat the heat exchange element forms a ribbed cooling body. In theembodiment, e.g. cooling air flows through the flow channels 51 in thedirection of their longitudinal axis which extends parallel to the baseplate 49, a chosen flow direction being indicated by way of example byan arrow 52. Furthermore, the general embodiments for FIG. 1 to 10 applycorrespondingly.

The described embodiments offer in addition to a significant increase ofthe output (power) an only small percentage increase in pressure losses.This is a consequence of the fact that, on the one hand, there is asubstantially greater, heat-exchanging surface and that the flow pathfor the fluid is correspondingly longer, whilst, on the other hand, theflow can follow the rounded flow channels easily. In addition, theadvantage in particular is produced that the tendency to become soiledin the flow channels is low despite the undulations because the broadsides delimiting the flow channels are continuously flat or slightlyrounded and smooth and no disruptive corners and angles are formed. Thisapplies even if the dimension of the overlapping of the undulations 6,described with reference to FIG. 2, is comparatively large so that theheat exchange elements of the described type are well suited above allto applications in the agricultural, forestry and building field. Inaddition, in particular those heat exchange elements, the walls of whichcomprise essentially flat portions, offer the advantage of being easilyproduced.

The invention is not restricted to the described embodiments which canbe modified in many ways. This applies above all to the indicated shapesand/or sizes of the different undulations and also to the density of thearrangement thereof. The choice of different parameters is extensivelydependent upon the individual case and the desired heat exchange or heattransfer output. In addition, it is possible to dispose the undulationsof adjacent walls in the flow direction at a preselected offset if, as aresult, the pressure losses are not increased in an undesired manner.Furthermore, the curved portions provided in the apexes of theundulations can have both a circular and an elliptical configuration orfollow other curves. It is clear furthermore that the invention can beapplied also to heat exchange elements other than those illustrated inthe drawings, configured e.g. as fins, and heat exchangers equipped withthese. Apart thereof, the given dimensions and/or inequalities should beused at least partly, with particular advantage however in a continuousmanner throughout the heat exchange elements produced therewith.Deviations of these dimensions and/or inequalities are, however, alsopossible within one and the same heat exchange element or heatexchanger. Finally it goes without saying that the different featurescan be combined with each other in a manner other than that describedand illustrated in the drawing.

It will be understood, that each of the elements described above or twoor more together, may also find a useful application in other types ofconstruction differing from the types described above.

While the invention has been illustrated and described as embodied in aheat exchange element and a heat exchanger, it is not intended to belimited to the details shown, since various modifications and structuralchanges may be made without departing in any way from the spirit of thepresent invention.

Without further analysis, the forgoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

1. Heat exchange element having adjacent, heat-transferring, smoothwalls (1, 11, 12, 20, 33, 46, 48) which, between each other, delimitflow channels (4, 41, 42, 51) with preselected channel widths (B) for atleast one fluid and are provided with undulations (6, 14) which protrudeon both sides and transversely relative to imaginary central planes (7),said undulations having preselected wavelengths (λ) and apexes (9 a, 9b) with radii of curvature (R) and apex spacings (W) measuredtransversely relative to said central planes (7), wherein an inequality0.1≦B/W≦0.55 applies at least partially to a ratio of said channel width(B) to said apex spacing (W) and wherein an inequality R≧1.2 B appliesat least partially to a ratio of said channel widths (B) to said radiusof curvature (R).
 2. Heat exchange element according to claim 1, whereinan inequality 0≦B/R≦0.75 applies to said ratio of channel width(B)/radius of curvature (R).
 3. Heat exchange element according to claim2, wherein an inequality 0.2≦B/R≦0.55 applies to said ratio of channelwidth (B)/radius of curvature (R).
 4. Heat exchange element according toclaim 1, wherein an inequality 0.35≦B/W≦0.50 applies to said ratio ofchannel width (B)/apex spacing (W).
 5. Heat exchange element accordingto claim 1, wherein an inequality 16 mm≦λ≦30 mm applies at leastpartially to said wavelength (λ).
 6. Heat exchange element according toclaim 1, wherein an inequality 2.4 mm≦R≦∞ applies at least partially tosaid radii of curvature (R), R=∞ corresponding to a wall portion (17)being disposed in a straight plane in the relevant apex and preferablyparallel to an associated central plane (7).
 7. Heat exchange elementaccording to claim 1, wherein said undulations (6, 14) have first flatportions (15, 16) which rise and fall in straight planes and at theapexes second wall portions which connect the first portions (15, 16)and are continuously curved or are modelled as a polygon.
 8. Heatexchange element according to claim 1, wherein said undulations (14)have first flat portions (15, 16) which rise and fall in straight planesand at the apexes second flat, straight wall portions (17) which connectsaid first portions (15, 16).
 9. Heat exchange element according toclaim 8, wherein said second flat wall portions (17) which are providedat the apexes are disposed parallel to said central planes (7).
 10. Heatexchange element according to claim 1, wherein said undulations haverespectively two half-waves (6 a, 6 b; 14 a, 14 b; 21 a, 21 b) which aredisposed on opposite sides of said central planes (7).
 11. Heat exchangeelement according to claim 10, wherein said half-waves (21 a, 21 b) areconnected by flat portions (22) which are disposed essentially in saidcentral planes (7).
 12. Heat exchange element according to claim 1,wherein said undulations (6, 14) have an identical configuration. 13.Heat exchange element according to claim 1, wherein said flow channels(4) have inlet and/or outlet ends (27, 28) for said fluid extendingessentially parallel to said central planes (7).
 14. Heat exchangeelement according to claim 1, wherein said undulations are provided withwavelengths (λ₁ to λ₃) and/or apex spacings (W₃ to W₅) which are ofdifferent sizes in a direction of said flow channels.
 15. Heat exchangeelement according to claim 1, wherein said walls (1, 11, 12, 20, 33, 46,48) have a thickness (S) of 0.08 m to 5 mm.
 16. Heat exchange elementaccording to claim 1, wherein said undulations (6, 14) are provided withwavelengths (λ) which are at least four times as great as said apexspacing (W).
 17. Heat exchange element according to claim 1, whereinsaid undulations (6, 14) of adjacent walls (1, 11, 12, 20, 33, 46, 48)are disposed without an offset relative to each other in a flowdirection.
 18. Heat exchange element according to claim 1, and being apart of a ribbed cooling body.
 19. Heat exchange element according toclaim 1, and being a part of a flat pipe heat exchanger.
 20. Heatexchange element according to claim 1, and being configured as a fin.21. Heat exchange element according to claim 1, and being configured asa lamella (corrugated rib) (32, 43, 44).
 22. Heat exchanger having atleast one heat exchange element according to claim 1.